It is unquestionably old in the art to provide means for forcing air because of its oxygen content into a vessel in which sewage or other such waste is passed through or treated to reduce the natural affinity toward oxygen found in sewage. This affinity is usually expressed as the biological oxygen demand (B.O.D.) in terms of parts per million of oxygen necessary to render the sewage nonseptic or innocuous to natural life, such as plant or fish life. Typical sewage may have about 100 to about 300 parts per million. Health departments usually require that this be reduced below 30 parts per million before the treated sewage is deposited in lakes or streams.
Typical aerators for this purpose are shown in U.S. Pat. Nos. . No. 3,149,071 (210-197) and 3,662,890 (210-195). Both these patents disclose waste treatment facilities wherein the BOD of the sewage liquid is reduced by pumping air directly into the sewage.
On the other hand, others, such as U.S. Pat. No. 1,963,354 (210-26), have suggested pumping air into an existing sewer line by providing a tank or manhole in the sewer line without interfering with the sewer line per se. U.S. Pat. No. 3,525,685 (210-15) provides an air line within the sewage line running from the point of collection to the point of treatment for supplying air into the moving sewage to prevent it from becoming septic and from building up undesirable sulfides, sulfates, methane gases and sulfuric acid, which can eventually destroy sewage lines. By forcing air into the moving sewage, stimulation of desirable aerobic bacteria growth is accomplished.
Rather than forcing air into moving sewage, U.S. Pat. No. 3,335,082 (210-15) suggests the drawing of air from a manhole through the sewage line to bring the sewage liquid into intimate contact with the air as well as remove obnoxious odors and gases from the sewer line.
Thus, the prior art recognizes the desirability of providing some aerating treatment within the sewage line between the source of the sewage and the treatment facility to not only control the build up of harmful and obnoxious gases, such as hydrogen sulphide and methane, as well as the formation of sulfates and sulfuric acid, but also to provide for secondary biological treatment by stimulating aerobic bacteria growth within the sewage as it is moving toward the primary treatment facility. This type of secondary treatment increases the capacity of the primary treatment facility by reducing the BOD in the sewage prior to its reaching the primary facility.
The present invention is directed to such a secondary "in-line" treatment apparatus to be provided in existing or newly built manholes in sewage lines between the source of the sewage and the primary treatment facility. The aerator apparatus of the present invention provides an inexpensive and simple structural means to cause the sewage to be placed in intimate and overall direct contact with air through the employment of an upstanding pipe end positioned centrally of the manhole to cause the gravity fed sewage to be directed upwardly within the manhole in the form of a fountain and flowed over the top of the conical ring and then splashed against the bottom of the manhole and thereafter drain down through an outlet where it is directed back into the sewage line. The secondary treatment apparatus suggested by U.S. Pat. Nos. 3,525,685 and 3,484,836 is costly, respectively requiring an air pump with a pipe line within the sewer line and a motor driven rotating disk member. While the structure of the present invention is intended to provide the same biological advantages desired in such secondary treatment, the present structure is much less expensive and has no moving parts which require maintenance and replacement, particularly those parts in direct contact with the sewage. Further, the structure herein disclosed has been found to be quite effective in reducing the BOD as compared to such secondary treatment facilities of the prior art since the sewage is caused to be forced upwardly within the manhole and splashed and sprayed about causing much more of the sewage liquid to be in overall direct contact with air than that provided by the structures shown in the above-mentioned two Patents.
U.S. Pat. No. 848,279 (210-150) does show the employment of an upwardly extended discharge pipe in a sewage treatment tank which is connected to relatively pure water supply, such as rain water, to direct the water upwardly in the tank to periodically cause decomposition of the mat formed on the top of the sewage and cause renewal of the aerobic bacteria growth in the tank by letting the air again be in intimate contact with the sewage liquid in the tank.